<国立科博専報>襲速紀地域を中心とした日本太平洋側フロラの特性について

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The species which are distributed in the Pacific side of Japan have been called the "Omote Nihon Element." Some are widely distributed throughout the entire region, but others are usually restricted to limestone or serpentine areas, to rocky places near rivers which often overflow and to poorly nourished or dry mountain ridges. Most of the latter species have usually been called the "Sohayaki Element" which is now regarded as a remnant of one of the most ancient floras of Japan. Data were gathered from field work to observe habitats and habits of the species and from studies of specimens deposited in the herbaria of Institutum Botanicum, Academia Sinica, Peking, China (PE), the University of Tokyo (TI), Tokyo Metropolitan University (Makino Herbarium : MAK), National Science Museum, Tokyo (TNS) and Kyoto University (KYO). Approximately 50 species (cited below) are examined in this paper from taxonomic and phytogeographic points of view. Based on habitat these species can be divided into two categories. 1. Plants growing on the steep cliffs only and/or on the shelf barrens. These species, protected from extinction by the habitat, are considered to have survived for long periods of time in competition with the invaders of both glacial and interglacial periods. Tanakaea radicans FR. & SAV., which grows on steep cliffs only (Fig. 1), is a representative species of this group and has a disjunct distribution on the Pacific side of Japan, eastern Shikoku and the southern part to the Chubu district of Honshu, but absent from the Kii Peninsula. Saussurea amabalis KITAMURA shows a similar disjunct pattern of distribution and grows on shelf barrens on the Pacific side of Japan. The species cited below are also considered to be relict, growing on shelf barrenes on the Pacific side of Japan : Pseudotsuga japonica (SHIRASAWA) BEISSN.; Alectorurus yedoensis (MAXIM.) MAKINO; Tricyrtis macrantha MAXIM. and subsp. macranthopsis (MASAM.) KITAMURA and T. ishiiana (KITAGAWA & T. KOYAMA) OHWI and var. surugensis YAMAZAKI; Hosta shikokiana N. FUJITA; H. hypoleuca MURATA, H. pulchella N. FUJITA; Lilium speciosum THUNBERG; Allium togashii HARA and A. virgunculae F. MAEKAWA & KITAMURA; Saxifraga sendaica MAXIM; Wikstroemia albiflora YATABE and W. kudoii MAKINO; Gentiana yakushimensis MAKINO; Aster komonoensis MAKINO and Saussurea pennata KOIDZ. 2. Plants referred to as "rheophytes" in Japan. Rheophyted was defined by van STEENIS (1932) based on plants in tropical areas. Although the mainland of Japan is located in the warm temperate zone, several species listed here are considered to occupy habitats similar to those of tropical plants which grow on rocky shelves near rivers in the bottoms of gorges which are innundated once to several times a year. They have in common such particular features of habit as follows : perennial or shrub, mostly with slender leaves and narrow branch or branchlet angles; roots which cling to the crevices of rocks anchoring the plant body against rushing water and sprouting immediately after a flood. These plants are resistant to physical damage but grow weakly in shade. Plants of this group are as follows : Osmunda lancea TUNBERG; Allium virgunculae F. MAEKAWA var. kiiense MURATA; Hosta kikutii F. MAEKAWA. var. caput-anis (F. MAEKAWA) F. MAEKAWA and var. polyneuron (F. MAEKAWA) N. FUJITA; Arundinella hirta (THUNBERG) C. TANAKA var. riparia (HONDA) OHWI; Alnus serrulatoides CALL.; Astilbe japonica (MORR. & DECNE.) A. GRAY; Spiraea tosaensis YATABE, S. japonica L. f. var. ripensis KITAMURA and S. thunbergii L.f. ex BLUME; Indigofera decora LINDL.; Angelica tenuisecta (MAKINO) MAKINO and A. shikokiana MAKINO ex YABE; Rhododendron indicum (L.) SWEET and R. ripense MAKINO; Leptodermis pulchella YATABE; Aster sohayakiensis KOIDZ., A. tenuipes MAKINO and A. ageratoides TURCZ. subsp. ripensis (MAKINO) KITAMURA and subsp. microcephalus (MIQ.) KITAMURA; Ixeris dentata (THUNBERG) NAKAI subsp. kitayamensis MURATA and Sol
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<国立科博専報>襲速紀地域を中心とした日本太平洋側フロラの特性について

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